Containment and Groundwater Modification
Team 3: Ajia, Amina, Darren, David, Domenico, Nicole, and Sruthi Overview
Groundwater zone contamination. More difficult to treat than surface water contamination Plume can spread to undesirable lengths and locations. “dissolved” or “free-phase” Containment = important in-situ step. Prevent the problem from escalating Followed by other treatment methods. Groundwater Modification = in-situ for the most part
Type 1: Isolation/Containment
● Passive vs Active
1) SLURRY WALLS High plasticity, low K
Sometimes 360° around
Sometimes capped on top
Floating OR Keyed in
Plume may react with wall
Steel Sheet Piles
Types: Bentonite+Soil, Cement+Bentonite, Polymers, Resins, Emulsions, Asphalts
Type 1: Isolation/Containment
1) Slurry Walls…
2) Soil Mixing
Penetration: fill in voids
1-3 m
Jet Grouting: destroy fabric
0.3-2 m
K: 10^-5 to 10^-8 cm/s
Type 1: Isolation/Containment
3) Sheet Piling
Joints are sealable
Risk: May crack aquicludes
Material costs
4) Active Controls
AFTER Containment,
Pump and treat
Other Methods like...
Type 2: Stabilization/Solidification
Stabilization: in-situ transformation (toxicity or solubility)
Solidification: creating solid mass to be taken out
In Situ Vitrification
electric current + heat to melt soil
becomes glass like material and traps contaminants Type 2: Stabilization/Solidification
Micro -encapsulation: trap contaminants in crystalline structure
(microscopic pores)
Or, Macro -encapsulation: trap on a solid surface
Organic vs Inorganic
Underlying mechanism: ADSORPTION
Strength + Durability
Permeability
Pumpability
Eventual leaching Type 3: Permeable Treatment Walls
Precipitation: Dissolved contaminant can react and “precipitate out” as a solid. It is pH-dependent.
METALS, hydroxides, sulfides, silicates, carbonates, phosphates
Detoxification: change contaminant into less toxic form
Ex: Cr+6 -> Cr+3
Biodegradation: Bacteria
Denitrification: Organic C
Sorption Influencing Factors
Things to consider:
Location
Aquifer
Public/Private Wells
Impermeable layer
http://www.waterincrisis.com/pages/aquifers_mn1/aquifers.html Contaminant Composition
Material (ex. Fly Ash)
Stress-deformation Analysis Influencing Factors
LNAPL:
Control the migration, not containment
Treatment wall
DNAPL:
May be used with other methods
Image reproduced from the EPA (Newell et al., 2015). Isolate the contaminant
Prevent lateral migration
Influencing Factors
Slurry Walls:
Bentonite Soil
Low conductivity with about 5-7% bentonite
High plasticity resists fractures
Backfill typically 2% bentonite
Sheet piles, geomembranes, or concrete cut-off as impermeable membrane
Bentonite Concrete
Brittle and may fracture
Fly ash to reduce degradation
Other materials: polymers, resins, emulsions and asphalts
Even more brittle
Influencing Factors
Table reproduced from the EPA (1992). Influencing Factors
Penetration and Jet Grouting:
Penetration
Support/stabilization Image courtesy of Keller Ground Engineering (2017). Jet
Soil/Slurry mix
Overlay columns
Conductivity of grout mix about 10^-5 to 10^-8 cm/s Influencing Factors
Figure reproduced from Pearlman (1999). Influencing Factors
Effects of pH on the system: Acidic Strong inorganics (pH < 1) Bentonite dissolution Silica Aluminum Basic Strong (pH > 11) Change the porosity
Image courtesy of CMI Sheet Piling (2017). Influencing Factors
Other Factors:
Some compounds may shrink the clay particles
Inorganic salts
Some organics
Freezing/thawing of the ground
Difficult to evaluate effectiveness
Only controls lateral migration
Needs to be compatible chemically Field Implementation
Impermeable Boundaries
1. Encompass DNAPL source area with barrier https://www.nap.edu/read/2311/chapter/4#52
OR
1. Dissolved plume is locally arrested with barriers
Implement through slurry walls, sheet piles, jet gravity, or pumping Field Implementation
Sheet Piles
Types: http://cmisheetpiling.com/applications/cut-off- containment/ - Steel
Formed by connecting the joints of adjacent sheet pile sections in sequential installation. Field Implementation
Pumping
Removes dissolved contaminants from the subsurface and prevent migration of contaminants https://frtr.gov/matrix2/section4/4-48.html
Uses a hydraulic barrier to prevent offsite migration of contaminant plumes
- Wells and piezometers are used to monitor the groundwater extraction system effectiveness Field Implementation
Slurry Wall
Specifics:
- Usually 2-4 feet thick
- Maximum of 200 feet deep
- Uses backfill of weathered shales, sand, clays, tills
Types of Slurry Walls:
- Soil-bentonite, cement-bentonite, soil-cement-bentonite, and a combination or use of composite systems http://www.geo-solutions.chttp://www.geoengineer.org/education/web-based-class-projects/39-web-based-class-projects/geoenvironmental-remediation- technologies/impermeable-barriersom/slurry-bentonite Field Implementation
Slurry Wall Construction of Soil-Bentonite Wall:
- Excavate soils contaminated with DNAPL and dispose or treat to clean
- Typically excavated with a long reach excavator under a bentonite water slurry
- Once the trench is completely excavated, dry bentonite, borrow soils, bentonite slurry and any other necessary additives are mixed together and added to the trench
- When the backfill operation is complete, the soil-bentonite backfill consolidates slightly and behaves like a soft clayey soil http://www.cetco.com/en-us/applications/ drilling-products/slurry-walls Field Implementation
Slurry Wall Construction of Soil-Bentonite Backfill:
- Backfill may be blended using a variety of equipment.
- Most common method is to mix batches of backfill alongside the slurry trench using a small excavator/bulldozer
- The resultant mix should look like wet concrete (low to moderate slump) and is placed into the trench Field Implementation
Slurry Wall Construction of Soil-Bentonite Backfill: Specifics:
- Permeability range: 10^-6 to 10^-8 cm/sec
- Low strength → will remain soft (in range of 300 psf) for design life https://theconstructor.org/geotechnical/jet-grouting-procedure-advantages/14470/
Field Implementation
Gravity Specifics:
- Particulate grouts include: clay, lime, fly ash, cement
- Chemical grouts include: Bitumen, resins, silicates
- Low viscosity is proportional to high penetration
- Jet Grouting: operate at 1-2 rpm, 1-2 ft^3/min, and 6,000 psi injection pressure
Video; http://www.haywardbaker.com/solutions/techniques/jet-grouting https://theconstructor.org/geotechnical/jet- grouting-procedure-advantages/14470/ Field Implementation
Gravity Implementation of Jet Grouting:
1. Soil treatment area is chosen and a hole is drilled to the required depth
a. 10-20 cm range
2. Jet grouting string is place over drill hole
a. 7-10 cm diameter string
3. String is raised and rotated slowly to seal the whole column surface with soil and the injected fluid system Field Implementation
Gravity Types of Jet Grouting Systems:
1. Single Fluid System: grout
2. Double Fluid System: Air + grout
3. Triple Fluid System: Water, air, and grout https://theconstructor.org/geotechnical/jet- grouting-procedure-advantages/14470/ https://www.youtube.com/watch? v=D_ncFvBljvk Field Implementation
Stabilization and Solidification (SS)
- Involves mixing a binding reagent into the contaminated media or waste
- This treatment relies on changes to the physical http://www.geoengineer.org/education/web- based-class-projects/geoenvironmental- properties of the waste as the cement solidifies remediation-technologies/stabilization- the waste solidification?showall=1&limitstart=
- Large concentrations of oils and greases (>20%) may prevent the hydration of cement Field Implementation
Stabilization and Solidification Types of Stabilization Methods:
1. In-situ stabilization: injection of stabilizing compounds into the soil
2. Ex-situ stabilization: involves excavation and backfilling Field Implementation
Common Field Implementation Steps In-situ Remediation
Also called in-situ soil mixing or auger mixing http://www.geo-solutions.com/soil-insitu- soil-stabilization-solidification There are three specific types of in-situ soil mixing:
1. Deep soil mixing (DSM)
2. Shallow soil mixing (SSM)
3. Backhoe stabilization
- Performed using a large diameter (3-12 ft) auger with mixing paddles and grout ports http://www.geo-solutions.com/soil-insitu- soil-stabilization-solidification Field Implementation
Common Field Implementation Steps
General In-situ Remediation Steps:
1. Addition of reagent
2. Mixing with backhoe until stabilization
3. Setting for 24-48 hours
4. Off-gas treatment to collect hazardous vapors http://www.geoengineer.org/education/web- based-class-projects/geoenvironmental- remediation-technologies/stabilization- Field Implementation solidification?showall=1&limitstart=
Common Field Implementation Steps
General In-situ Remediation Steps:
- Portland cement is the most common reagent, but others include blast furnace slag, fly ash, cement kiln dust, and bentonite. Field Implementation
Common Field Implementation Steps Ex-situ Remediation
- Provide better control over reagents, mixing, and sampling
Important considerations:
- Swelling during mixing
- Generation of harmful odors, dust, and organic vapors Field Implementation
Common Field Implementation Steps Ex-situ Remediation: Mobile Mixing
Typical procedure of mobile mixing includes:
1. Excavation to remove contaminated waste
2. Classification of wastes
3. Mobile plant setup and mixing
4. Off-gas treatment to collect hazardous vapors
5. Final disposal http://www.geoengineer.org/education/web-based-class-projects/geoenvironmental- remediation-technologies/stabilization-solidification?showall=1&limitstart= Field Implementation
Typical mobile mixing plant schematic. Field Implementation
Common Field Implementation Steps Ex-situ Remediation: In-Drum Mixing
Typical procedure of mobile mixing includes:
1. Evaluation/identification of contents in each drum
2. Evaluation of drum condition and head space
3. Preparation of materials handling location
4. Addition and mixing of SS chemicals
5. Placement of drums in a secure area for curing
6. Addition of inert material to any remaining headspace
7. Final disposal of drums Field Implementation
Permeable Treatment Walls
Highly specialized type of slurry wall construction, which can be an economical alternative for applying chemical reagents to contaminated groundwater http://www.geo-solutions.com/permeable- - Can be installed using the biopolymer slurry reactive-barriers trenching (BP Trench) method, shallow soil mixing or conventional open-cut trenching Field Implementation
Permeable Treatment Walls
- Permeability of the application is controlled so the wall exhibits a hydraulic conductivity similar to the surrounding native soils, allowing groundwater to flow naturally through the barrier
- Chemical reagents are added to the installation at the time of construction within the barrier or injected later through the well installed for that purpose
Typical reagents include:
- Zero valent iron, activated carbon, peat moss, etc Field Implementation
Permeable Treatment Walls
Zero Valent Iron Treatment:
- Treats contaminants such as organic halogenated hydrocarbons, inorganics, and metals
- Reaction degrades or precipitates out contaminants
Permeable Treatment Wall Construction:
- Vertical hydrofracturing
- Ideal in urban areas
Case Study #1 : Soil-Bentonite Cutoff Wall through an Abandoned Coal Mine
Approximately 18 acre superfund site in Grove City, PA
Abandoned strip mine
Adjacent to deep mine and highwall
Partially flooded
Surrounding area is mostly agricultural, some residential area 250m north
Mine operated between 1900’s and 1940’s
Used as a disposal site from 1950’s to 1978
Foundry sand, slag, and scrap metal
Wood
Paper
Plastic
Drums of waste (already removed)
Case Study #1
Added to NPL in 1984
Contaminants found:
benzo(a)pyrene
dibenzo(a,h)anthracene
chromium
Lead
Nickel
TCE and vinyl chloride
Arsenic Case Study #1
EPA concluded site had contaminated groundwater
Most of the waste deposited below water table
Onsite waste material considered to be a dermal contact risk
Contaminated groundwater migration considered to be a future risk
Case Study #1
Remedial Objectives:
Prevent migration of contamination through groundwater
Prevent infiltration of surface water into contaminated area
Prevent contact with contaminated materials
EPA preferred RCRA compliance landfill
Would have achieved objectives but estimated cost of $26 million
Included excavating and stockpiling waste onsite while RCRA cell was completed elsewhere
Cost would be high due to requiring a dewatering system and wastewater treatment Case Study #1
Alternative remedial action proposed by the engineer
Soil-bentonite slurry wall around contaminated area
Low permeability GCL cap
Extraction wells installed inside the slurry cutoff wall collect groundwater and send to onsite treatment system
Estimated cost $10 million
EPA would not approve unless conditions were met
Verification of coal seam underclay along entire slurry wall location
Demonstration that remedy could control damage to cutoff wall or cap due to subsidence
Demonstrate that remedy would not adversely affect mine pool and had reasonable cost
Case Study #1
Site was not ideal for slurry wall technique due to presence of mine voids as high as 8 ft
Mine grouting was the technique selected to fill the voids
Contains the slurry wall
Protects slurry wall and cap from damage in case of subsidence
Case Study #1
Three parallel lines of grouting were installed using air rotary drilling rigs and grout mixture prepared to 100 psi minimum strength
Slurry wall was keyed into either Brookeville Coal Underclay or Homewood sandstone
Formations helped create confining zone
Case Study #1 Case Study #1 Case Study #1
Project was completed from 1995-1997
Remediation costs were reduced by 60% due to onsite containment versus removal to off site RCRA landfill
Project illustrated ability of slurry cutoff walls to be an effective option through areas with voids such as mines
Case Study 2: Design and Construction of a Slurry Wall around Superfund Site
Ellis Street Site
June - October, 1987
Mountain View, California (“Silicon Valley”)
Total Area: 1000 ft by 840 ft
Groundwater level 20 ft below, 50 ft above sea level
Owned by Raytheon Company, Semiconductor Division
Placed on EPA NPL list due to presence of contaminants in the ground/groundwater
Operating facility, equipment sensitivities to vibrations and dust
Surrounding area: Immediate area is paved, western half is undeveloped open area
Case Study 2
Investigation:
200 boreholes, 100 monitoring and extraction wells
Soil consistency: medium dense to dense interbedded clays, silts, sands and gravels
Contaminants:
Trichloroethylene (TCE)
1, 2-dichloroethylene (1, 2-DCE)
<37 ppm in soil, <200 mg/L in groundwater
Remedial Objectives:
Stop further migration of chemicals in a complex aquifer system
To facilitate the removal of possible chemical sources from saturated zones beneath Case Study 2
Slurry Wall with Pumping from within Contained Area
Maintain inward and upward hydraulic gradients
Halt further migration of contaminants
Protect underlying aquifer system
Facilitate the removal of saturated soils
Allowed facilities to remain operational during all stages of construction
Alternatives Methods
Excavation
Groundwater Control Case Study 2
Design
Total perimeter: 3400 ft
Max. hydraulic conductivity: 1.0 * 10-7 cm/s
Utility Protection
15 ft clearance under utility bridge
Slurry wall 30 ft from property boundary
Monitoring wells
Bentonite Slurry Wall
Min. density of 70 pcf
Width: min. 3 feet
Depth: 100 ft Case Study 2
Effects and Results
Met specified permeability
Water levels in pumped aquifers decreased upon completion
Prevention of further off-site contamination
No disruption to facility operations or production
Successful completion in more restrictive setting
Applicability and Limitations
Slurry Walls
Does not treat or destroy contaminant
Test and monitoring necessary
Seismic activities and pressure effect
Groundwater control
Designing Applicability and Limitations
Applicabilities of slurry walls
Does not target a particular group of contaminant
Deals with a wide variety of contaminant
Deals with large waste mass
Applicability and Limitations
Sheet Piling
Susceptible to salts and acids
Interlock leakage
High cost
Installation difficulties Applicability and Limitations
Applicabilities of sheet piling
Easy replacement
Depth advantage
Quick installation
Little waste material during installation
Reduced diffusion transport
Applicability and Limitations
Permeable Treatment Walls
Ensuring total capture can be difficult
Time consuming/Monitoring system
Reduced effectiveness over long-term
Reactive material leach
Installation difficulties (Sheet piles) Applicability and Limitations
Applicability of PRBs
Wide range of contaminants
No loss of ground water
Little to no energy requirement Availability- Slurry Wall
Cement Bentonite- common form of vertical barriers in Europe
Seepage control especially
Soil Bentonite- most used technique for contamination for the US
Soil-Cement-Bentonite- mix of the two above and not nearly as popular as either. Cost- Slurry Wall
Cement- Bentonite wall ranges from $10-20/ft2
2 ft wide barrier of less than 100 ft
Soil-Bentonite wall ranges from $5-7/ft2
Costs not including cost needed for
Chemical analyses
Feasibility test
Compatibility test
Easily variable cost Availability- Grouting
Best used in lower permeability soils
Different types of grout (different viscosity) are to be used for different permeabilities of soil
Availability- Grouting
Jet Grouting
Done at high Pressure
Single
Uses existing soil and grout to create impermeable wall
Double
Uses air and grout
Clears jet stream of soil and groundwater
Triple
Uses Water, air and grout
Cuts out soil and lifts it so that the wall can be made of pure grout
Availability- Grouting
Permeation grouting
Done at low pressure
Best used if you do not want to change structure of soil
Applicable for rock
Viable for both short and long term applications Cost- Jet Grouting
Mobilizing Equipment
Over $35,000 per rig
Labor and materials
$320/m3 of improved ground
Handling, removal, and disposal of waste slurry
System dependant
Slurry Produced is 60-100% of volume of treated soil Cost- Permeation Grouting
Mobilizing Equipment
Microfine cement grout$15,00-25,000
Sodium silicate grout- Over $25,000
Installing Sleeve Port
$50 per meter of pipe
Labor and grout materials
Microfine- $130/m3 of treated ground
Silicate- $200/m3 of treated ground Availability- In Situ Soil Mixing
With regard to soil type
High in clean granular soils
Low in clayey soils
Best if you do not want to move soil
Very few in the United States
Cost- In Situ Soil Mixing
$100,000 for rig and grout plant
Grout materials and mixing
$100/m3 of improved ground for shallow mixing (<8 m)
$200/m3 of improved ground for deep mixing (8-30 m)
Discarding of waste soil-cement
About 30% of treated volume Availability & Cost Permeable Treatment Wall
Best for
Shallow deposits (0-70 ft)
Unconfined aquifer systems in unconsolidated deposits
If reactive material is more conductive than the aquifer
Average capital cost
$460,000